Not so. When the United States made a land grab in 1848 there was no international law forbidding the acquisition of land thru war. This changed after the Second World War and was in place in 1967 when the Israelis moved into the West Bank, including East Jerusalem.Would be like askin' us...
... to give back the territory gained...
... in the Mexican-American War.
It was formalised after WW2 but was part of the customary laws of war, much earlier.
Date and venue when this took place ?